HFS+ is extensible, so there have been extensions rolled out over time. This means that any older HFS+ partition is forwards-compatible, but newer features (Case insensitivity, journalling, ACLs, hardlinked folders, compression and encryption) are not handled/recognized if a newer partition is mounted under an older OS.

So yeah; HFS+, as it debuted in 1998, is the same filesystem that will be used in macOS 10.12, and will possibly even still be the default for 10.13 in 2017. We might see it deprecated in 2018, *20 years* after it was first deployed, but APFS still has a few kinks to work out before that happens, and all currently supported versions of macOS will need to support APFS -- so since Apple supports 3 versions back, we're more likely to see it show up as the default in 10.14 or 10.15.

Would be a bad day to see HFS+ being dropped by Apple, but no surprise. HFS+ must be the last major part of the OS offering backward compatibility for emulators.Sure its nonsense to address a NAND device via sATA as if it was a spinning disk.OS X is still THE host for Mac emulators, 10.9 or lower were best though.The day APFS is implemented as the sole filesystem, a Mac will be worse than Windows for emulators.

It won't be that bad; Apple already dropped support for MFS and HFS, and we're still surviving. FUSE plugins help; hfsfuse already supports HFS+. For me, the scary thing is if they ever drop support for named forks -- that means that it won't matter if you can mount the filesystem, as the OS will no longer be able to actually access the data in non-data forks. And that's not something easily fixable with a FUSE plugin.